The roles of small RNA-protein complexes (RNPs) in gene expression or other aspects of mammalian cell metabolism will be probed using patient autoantibodies. Structures of the small nuclear ribonucleoproteins (snRNPs) containing U2, U4, U5 and U6 RNAs will be defined by additional fractionation and analysis of their protein moieties, cloning of the genes for certain protein and RNA components, and demonstrating that U4 and U6 RNAs coexist in a single particle. Potential functions for these snRNPs will be sought using antibodies and in vitro systems active in mRNA splicing, other RNA processing events, or RNA transcription, and by studying the interaction of purified snRNP particles with RNA substrates containing possible recognition sites. Drosophila genes for U2, U4, U5 and U6 will also be cloned to allow us to take advantage of certain aspects of that system. The nucleic acid components of another nuclear antigen, Ku, which appears to contain both DNA and RNA, will be analyzed. A 5S rRNA-containing nucleolar RNP, which behaves as an intermediate in ribosome biogenesis, will be further defined with respect to its protein component(s) and its possible role in regulating the transcription of rRNA. The Ro small cytoplasmic RNPs (scRNPs) will be analyzed by 1) defining where the Ro protein binds to the RNAs, 2) examining how conserved the RNA sequences are in human versus mouse cells, 3) delineating their distribution in cells and tissues, and 4) using antibodies to ask whether Ro scRNPs regulate translation of any particular class of mRNAs. We will ascertain whether we have identitifed a centriolar small RNP by preparing a cDNA clone of the RNA for use as an in situ hybridization probe. Finally, we shall obtain monclonal antibodies and continue to screen patient sera for new specifities directed against small RNPs. Defining the structures and cellular functions of the various small RNPs that are frequently targets of the autoimmune response should provide new insights into the pathogenesis of rheumatic disease.